Psilocybin ( Drugs / Substance Abuse)

Psilocybin is a naturally occurring psychedelic compound produced by more than 200 species of mushrooms, collectively known as psilocybin mushrooms. The most potent are members of the genus Psilocybe, such as P. azurescens, P. semilanceata, and P. cyanescens, but psilocybin has also been isolated from about a dozen other genera. As a prodrug, psilocybin is quickly converted by the body to psilocin, which has mind-altering effects similar (in some aspects) to those of LSD, mescaline, and DMT. The effects generally include euphoria, visual and mental hallucinations, changes in perception, a distorted sense of time, and spiritual experiences, and can include possible adverse reactions such as nausea and panic attacks.

Imagery found on prehistoric murals and rock paintings of modern-day Spain and Algeria suggest that human usage of psilocybin mushrooms dates back thousands of years. In Mesoamerica, the mushrooms had long been consumed in spiritual and divinatory ceremonies before Spanish chroniclers first documented their use in the 16th century. In a 1957 Life magazine article, American banker and ethnomycologist R. Gordon Wasson described his experiences ingesting psilocybin-containing mushrooms during a traditional ceremony in Mexico, introducing the drug to popular culture. Shortly afterward, the Swiss chemist Albert Hofmann isolated the active principle psilocybin from the mushroom Psilocybe mexicana. Hofmann’s employer Sandoz marketed and sold pure psilocybin to physicians and clinicians worldwide for use in psychedelic psychotherapy. Although increasingly restrictive drug laws of the late 1960s curbed scientific research into the effects of psilocybin and other hallucinogens, its popularity as an entheogen (spirituality-enhancing agent) grew in the next decade, largely owing to the increased availability of information on how to cultivate psilocybin mushrooms.

Some users of the drug consider it an entheogen and a tool to supplement practices for transcendence, including meditation and psychonautics. The intensity and duration of the effects of psilocybin are variable, depending on species or cultivar of mushrooms, dosage, individual physiology, and set and setting, as was shown in experiments led by Timothy Leary at Harvard University in the early 1960s. Once ingested, psilocybin is rapidly metabolized to psilocin, which then acts on serotonin receptors in the brain. The mind-altering effects of psilocybin typically last from two to six hours, although to individuals under the influence of psilocybin, the effects may seem to last much longer, since the drug can distort the perception of time. Psilocybin has a low toxicity and a relatively low harm potential, and reports of lethal doses of the drug are rare. Several modern bioanalytical methods have been adapted to rapidly and accurately screen the levels of psilocybin in mushroom samples and body fluids. Since the 1990s, there has been a renewal of scientific research into the potential medical and psychological therapeutic benefits of psilocybin for treating conditions including obsessive-compulsive disorder, cluster headaches, and anxiety related to terminal cancer. Possession of psilocybin-containing mushrooms has been outlawed in most countries, and it has been classified as a scheduled drug by many national drug laws.

Psilocybin is present in varying concentrations in over 200 species of Basidiomycota mushrooms. In a 2000 review on the worldwide distribution of hallucinogenic mushrooms, Gastón Guzmán and colleagues considered these to be distributed amongst the following genera: Psilocybe (116 species), Gymnopilus (14), Panaeolus (13), Copelandia (12), Hypholoma (6), Pluteus (6), Inocybe (6), Conocybe (4), Panaeolina (4), Gerronema (2) and Agrocybe, Galerina and Mycena (1 species each). Guzmán increased his estimate of the number of psilocybin-containing Psilocybe to 144 species in a 2005 review. The majority of these are found in Mexico (53 species), with the remainder distributed in the US and Canada (22), Europe (16), Asia (15), Africa (4), and Australia and associated islands (19). In general, psilocybin-containing species are dark-spored, gilled mushrooms that grow in meadows and woods of the subtropics and tropics, usually in soils rich in humus and plant debris. Psilocybin mushrooms occur on all continents, but the majority of species are found in subtropical humid forests. Psilocybe species commonly found in the tropics include P. cubensis and P. subcubensis. P. semilanceata—considered by Guzmán to be the world’s most widely distributed psilocybin mushroom—is found in Europe, North America, Asia, South America, Australia and New Zealand, but is entirely absent from Mexico. Although the presence or absence of psilocybin is not of much use as a chemotaxonomical marker at the familial level or higher, it is used to classify taxa of lower taxonomic groups.

Both the caps and the stems contain the psychoactive compounds, although the caps contain consistently more. The spores of these mushrooms do not contain psilocybin or psilocin. The total potency varies greatly between species and even between specimens of a species collected or grown from the same strain. Because most psilocybin biosynthesis occurs early in the formation of fruit bodies or sclerotia, younger, smaller mushrooms tend to have a higher concentration of the drug than larger, mature mushrooms. In general, the psilocybin content of mushrooms is quite variable (ranging from almost nothing to 1.5% of the dry weight) and depends on species, strain, growth and drying conditions, and mushroom size. Cultivated mushrooms have less variability in psilocybin content than wild mushrooms. The drug is more stable in dried than fresh mushrooms; dried mushrooms retain their potency for months or even years, while mushrooms stored fresh for four weeks contain only traces of the original psilocybin. The psilocybin contents of dried herbarium specimens of Psilocybe semilanceata in one study were shown to decrease with the increasing age of the sample: collections dated 11, 33, or 118 years old contained 0.84%, 0.67%, and 0.014% (all dry weight), respectively. Mature mycelia contain some psilocybin, while young mycelia (recently germinated from spores) lack appreciable amounts. Many species of mushrooms containing psilocybin also contain lesser amounts of the analog compounds baeocystin and norbaeocystin, chemicals thought to be biogenic precursors. Although most species of psilocybin-containing mushrooms bruise blue when handled or damaged due to the oxidization of phenolic compounds, this reaction is not a definitive method of identification or determining a mushroom’s potency.

Toxicity And Harm Potential


The toxicity of psilocybin is low. In rats, the median lethal dose (LD50) when administered orally is 280 milligrams per kilogram (mg/kg), approximately one and a half times that of caffeine. When administered intravenously in rabbits, psilocybin’s LD50 is approximately 12.5 mg/kg. Psilocybin comprises approximately 1% of the weight of Psilocybe cubensis mushrooms, and so nearly 1.7 kilograms (3.7 lb) of dried mushrooms, or 17 kilograms (37 lb) of fresh mushrooms, would be required for a 60-kilogram (130 lb) person to reach the 280 mg/kg LD50 value of rats. Based on the results of animal studies, the lethal dose of psilocybin has been extrapolated to be 6 grams, 1000 times greater than the effective dose of 6 milligrams. The Registry of Toxic Effects of Chemical Substances assigns psilocybin a relatively high therapeutic index of 641 (higher values correspond to a better safety profile); for comparison, the therapeutic indices of aspirin and nicotine are 199 and 21, respectively. The lethal dose from psilocybin toxicity alone is unknown at recreational or medicinal levels, and has rarely been documented—as of 2011, only two cases attributed to overdosing on hallucinogenic mushrooms (without concurrent use of other drugs) have been reported in the scientific literature.

Most of the comparatively few fatal incidents reported in the literature that are associated with psychedelic mushroom usage involve the simultaneous use of other drugs, especially alcohol. Probably the most common cause of hospital admissions resulting from magic mushroom usage involve “bad trips” or panic reactions, in which affected individuals become extremely anxious, confused, agitated, or disoriented. Accidents, self-injury, or suicide attempts can result from serious cases of acute psychotic episodes.

Repeated use of psilocybin does not lead to physical dependence. A 2008 study concluded that, based on US data from the period 2000–2002, adolescent-onset (defined here as ages 11–17) usage of hallucinogenic drugs (including psilocybin) did not increase the risk of drug dependence in adulthood; this was in contrast to adolescent usage of cannabis, cocaine, inhalants, anxiolytic medicines, and stimulants, all of which were associated with “an excess risk of developing clinical features associated with drug dependence”. Similarly, a 2010 Dutch study ranked the relative harm of psilocybin mushrooms compared to a selection of 19 recreational drugs, including alcohol, cannabis, cocaine, ecstasy, heroin, and tobacco. Magic mushrooms were ranked as the illicit drug with the lowest harm, corroborating conclusions reached earlier by expert groups in the United Kingdom.

Although no studies have linked psilocybin with birth defects, it is recommended that pregnant women avoid its usage.



Although psilocybin may be prepared synthetically, outside of the research setting, it is not typically used in this form. The psilocybin present in certain species of mushrooms can be ingested in several ways: by consuming fresh or dried fruit bodies, by preparing a tisane, or by combining with other foods to mask the bitter taste. In rare cases people have injected mushroom extracts intravenously. The effects of the drug begin 10–40 minutes after ingestion, and last 2–6 hours depending on dose, species, and individual metabolism.The half life of psilocybin is 163 ± 64 minutes when taken orally, or 74.1 ± 19.6 minutes when injected intravenously. A dosage of 4–10 mg, corresponding roughly to 50–300 micrograms per kilogram (µg/kg) of body weight, is required to induce psychedelic effects. A typical recreational dosage is 10–50 mg psilocybin, which is roughly equivalent to 10–50 grams of fresh mushrooms, or 1–5 grams of dried mushrooms. A small number of people are unusually sensitive to psilocybin, such that a normally threshold-level dose of about 2 mg can result in effects usually associated with medium or high doses. In contrast, there are some who require relatively high doses to experience noticeable effects. Individual brain chemistry and metabolism play a large role in determining a person’s response to psilocybin.

Psilocybin is metabolized mostly in the liver. As it becomes converted to psilocin, it undergoes a first-pass effect, whereby its concentration is greatly reduced before it reaches the systemic circulation. Psilocin is broken down by the enzyme monoamine oxidase to produce several metabolites that can circulate in the blood plasma, including 4-hydroxyindole-3-acetaldehyde, 4-hydroxytryptophol, and 4-hydroxyindole-3-acetic acid.Some psilocin is not broken down by enzymes, and instead forms a glucuronide; this is a biochemical mechanism animals use to eliminate toxic substances by linking them with glucuronic acid, which can then be excreted in the urine. Psilocin is glucuronated by the glucuronosyltransferase enzymes UGT1A9 in the liver, and by UGT1A10 in the small intestine. Based on studies using animals, about 50% of ingested psilocybin is absorbed through the stomach and intestine. Within 24 hours, about 65% of the absorbed psilocybin is excreted into the urine, and a further 15–20% is excreted in the bile and feces. Although most of the remaining drug is eliminated in this way within 8 hours, it is still detectable in the urine after 7 days. Clinical studies show that psilocin concentrations in the plasma of adults average about 8 µg/liter within 2 hours after ingestion of a single 15 mg oral psilocybin dose; psychological effects occur with a blood plasma concentration of 4–6 µg/liter. Psilocybin is about 100 times less potent than LSD on a weight per weight basis, and the physiological effects last about half as long.

Tolerance to psilocybin builds and dissipates quickly; ingesting psilocybin more than about once a week can lead to diminished effects. Tolerance dissipates after a few days, so doses can be spaced several days apart to avoid the effect. A cross-tolerance can develop between psilocybin and the pharmacologically similar LSD, and between psilocybin and phenethylamines such as mescaline and DOM. Monoamine oxidase inhibitors (MAOI) have been known to prolong and enhance the effects of psilocybin. Alcohol consumption may enhance the effects of psilocybin, because acetaldehyde, one of the primary breakdown metabolites of consumed alcohol, reacts with biogenic amines present in the body to produce MAOIs related to tetrahydroisoquinoline and β-carboline. Tobacco smokers can also experience more powerful effects with psilocybin, because tobacco smoke exposure decreases levels of MAO in the brain and peripheral organs.

The effects of psilocybin are highly variable and depend on the mindset and environment in which the user has the experience, factors commonly referred to as set and setting. In the early 1960s, Timothy Leary and colleagues at Harvard University investigated the role of set and setting on the effects of psilocybin. They administered the drug to 175 volunteers from various backgrounds in an environment intended to be similar to a comfortable living room. Ninety-eight of the subjects were given questionnaires to assess their experiences and the contribution of background and situational factors. Individuals who had experience with psilocybin prior to the study reported more pleasant experiences than those for whom the drug was novel. Group size, dosage, preparation, and expectancy were important determinants of the drug response. Those placed in groups of more than eight individuals generally felt that the groups were less supportive, and their experiences were less pleasant. Conversely, smaller groups (fewer than six individuals) were seen as more supportive. Participants also reported having more positive reactions to the drug in those groups. Leary and colleagues proposed that psilocybin heightens suggestibility, making an individual more receptive to interpersonal interactions and environmental stimuli. These findings were affirmed in a later review by Jos ten Berge (1999), who concluded that dosage, set, and setting were fundamental factors in determining the outcome of experiments that tested the effects of psychedelic drugs on artists’ creativity.
After ingesting psilocybin, a wide range of subjective effects may be experienced: feelings of disorientation, lethargy, giddiness, euphoria, joy, and depression. About a third of users report feelings of anxiety or paranoia. Low doses of the drug can induce hallucinatory effects. Closed-eye hallucinations may occur, in which the affected individual sees multicolored geometric shapes and vivid imaginative sequences. Some individuals report experiencing synesthesia, such as tactile sensations when viewing colors. At higher doses, psilocybin can lead to “Intensification of affective responses, enhanced ability for introspection, regression to primitive and childlike thinking, and activation of vivid memory traces with pronounced emotional undertones”. Open-eye visual hallucinations are common, and may be very detailed although rarely confused with reality.

A 2011 prospective study by Roland R. Griffiths and colleagues suggests that a single high dosage of psilocybin can cause long-term changes in the personality of its users. About half of the study participants—described as healthy, “spiritually active”, and many possessing postgraduate degrees—showed an increase in the personality dimension of openness (assessed using the Revised NEO Personality Inventory), and this positive effect was apparent more than a year after the psilocybin session. According to the study authors, the finding is significant because “no study has prospectively demonstrated personality change in healthy adults after an experimentally manipulated discrete event.” Although other researchers have described instances of psychedelic drug usage leading to new psychological understandings and personal insights, it is not known whether these experimental results can be generalized to larger populations.

Physical Effects
Common responses include: pupil dilation (93%); changes in heart rate (100%), including increases (56%), decreases (13%), and variable responses (31%); changes in blood pressure (84%), including hypotension (34%), hypertension (28%), and general instability (22%); changes in stretch reflex (86%), including increases (80%) and decreases (6%); nausea (44%); tremor (25%); and dysmetria (16%) (inability to properly direct or limit motions). The temporary increases in blood pressure caused by the drug can be a risk factor for users with pre-existing hypertension.These qualitative somatic effects caused by psilocybin have been corroborated by several early clinical studies. A 2005 magazine survey of club goers in the UK found that nausea or vomiting was experienced by over a quarter of those who had used hallucinogenic mushrooms in the last year, although this effect is caused by the mushroom rather than psilocybin itself. In one study, administration of gradually increasing dosages of psilocybin daily for 21 days had no measurable effect on electrolyte levels, blood sugar levels, or liver toxicity tests.

Perceptual Distortions
Psilocybin is known to strongly influence the subjective experience of the passage of time.Users often feel as if time is slowed down, resulting in the perception that “minutes appear to be hours” or “time is standing still”.Studies have demonstrated that psilocybin significantly impairs subjects’ ability to gauge time intervals longer than 2.5 seconds, impairs their ability to synchronize to inter-beat intervals longer than 2 seconds, and reduces their preferred tapping rate.These results are consistent with the drug’s role in affecting prefrontal cortex activity, and the role that the prefrontal cortex is known to play in time perception. However, the neurochemical basis of psilocybin’s effects on the perception of time are not known with certainty.

Users having a pleasant experience can feel a sense of connection to others, nature, and the universe; other perceptions and emotions are also often intensified. Users having an unpleasant experience (a “bad trip”) describe a reaction accompanied by fear, other unpleasant feelings, and occasionally by dangerous behavior. In general, the phrase “bad trip” is used to describe a reaction that is characterized primarily by fear or other unpleasant emotions, not just transitory experience of such feelings. A variety of factors may contribute to a psilocybin user experiencing a bad trip, including “tripping” during an emotional or physical low or in a non-supportive environment (see: set and setting). Ingesting psilocybin in combination with other drugs, including alcohol, can also increase the likelihood of a bad trip. Other than the duration of the experience, the effects of psilocybin are similar to comparable dosages of LSD or mescaline. However, in the Psychedelics Encyclopedia, author Peter Stafford noted, “The psilocybin experience seems to be warmer, not as forceful and less isolating. It tends to build connections between people, who are generally much more in communication than when they use LSD.”

Possible Adverse Psychiatric Effects
Panic reactions can occur after consumption of psilocybin-containing mushrooms, especially if the ingestion is accidental or otherwise unexpected. Reactions characterized by violence, aggression, homicidal and suicidal attempts, prolonged schizophrenia-like psychosis, and convulsions have been reported in the literature. A 2005 survey conducted in the United Kingdom found that almost a quarter of those who had used psilocybin mushrooms in the past year had experienced a panic attack. Other adverse effects less frequently reported include paranoia, confusion, derealization, disconnection from reality, and mania. Psilocybin usage can temporarily induce a state of depersonalization disorder.Usage by those with schizophrenia can induce acute psychotic states requiring hospitalization.

The similarity of psilocybin-induced symptoms to those of schizophrenia has made the drug a useful research tool in behavioral and neuroimaging studies of this psychotic disorder. In both cases, psychotic symptoms are thought to arise from a “deficient gating of sensory and cognitive information” in the brain that ultimately lead to “cognitive fragmentation and psychosis”.Flashbacks (spontaneous recurrences of a previous psilocybin experience) can occur long after having used psilocybin mushrooms. Hallucinogen persisting perception disorder (HPPD) is characterized by a continual presence of visual disturbances similar to those generated by psychedelic substances. Neither flashbacks nor HPPD are commonly associated with psilocybin usage, and correlations between HPPD and psychedelics are further obscured by polydrug use and other variables.

Social And Legal Aspects
A 2009 national survey of drug use by the US Department of Health and Human Services concluded that the number of first-time psilocybin mushroom users in the United States was roughly equivalent to the number of first-time users of marijuana. In European countries, the lifetime prevalence estimates of psychedelic mushroom usage among young adults (15–34 years) range from 0.3% to 14.1%. In modern Mexico, traditional ceremonial use survives among several indigenous groups, including the Nahuatls, the Matlazinca, the Totonacs, the Mazatecs, Mixes, Zapotecs, and the Chatino. Although hallucinogenic Psilocybe species are abundant in low-lying areas of Mexico, most ceremonial use takes places in mountainous areas of elevations greater than 1,500 meters (4,900 ft). Guzmán suggests this is a vestige of Spanish colonial influence from several hundred years earlier, when mushroom use was persecuted by the Catholic Church.

In the United States, psilocybin (and psilocin) were first subjected to federal regulation by the Drug Abuse Control Amendments of 1965, a product of a bill sponsored by Senator Thomas J. Dodd. The law—passed in July 1965 and effected on February 1, 1966—was an amendment to the federal Food, Drug and Cosmetic Act and was intended to regulate the unlicensed “possession, manufacture, or sale of depressant, stimulant and hallucinogenic drugs”.The statutes themselves, however, did not list the “hallucinogenic drugs” that were being regulated. Instead, the term “hallucinogenic drugs” was meant to refer to those substances believed to have a “hallucinogenic effect on the central nervous system”.

Despite the seemingly strict provisions of the law, many people were exempt from prosecution. The statutes “permit … people to possess such drugs so long as they were for the personal use of the possessor, [for] a member of his household, or for administration to an animal”. The federal law that specifically banned psilocybin and psilocin was enacted on October 24, 1968. The substances were said to have “a high potential for abuse”, “no currently accepted medical use,” and “a lack of accepted safety”.On October 27, 1970, both psilocybin and psilocin became classified as Schedule I drugs and were simultaneously labeled “hallucinogens” under a section of the Comprehensive Drug Abuse Prevention and Control Act known as the Controlled Substances Act.Schedule I drugs are illicit drugs that are claimed to have no known therapeutic benefit. The United Nations Convention on Psychotropic Substances (adopted in 1971) requires its members to prohibit psilocybin, and parties to the treaty are required to restrict use of the drug to medical and scientific research under strictly controlled conditions. However, the mushrooms containing the drug were not specifically included in the convention, due largely to pressure from the Mexican government. Most national drug laws have been amended to reflect the terms of the convention; examples include the UK Misuse of Drugs Act 1971, the US Psychotropic Substances Act of 1978, the Canadian Controlled Drugs and Substances Act of 1996,and the Japanese Narcotics and Psychotropics Control Law of 2002. The possession and use of psilocybin is prohibited under almost all circumstances, and often carries severe legal penalties.

Possession and use of psilocybin mushrooms, including the bluing species of Psilocybe, is therefore prohibited by extension. However, in many national, state, and provincial drug laws, there has been a great deal of ambiguity about the legal status of psilocybin mushrooms, as well as a strong element of selective enforcement in some places. Most US state courts have considered the mushroom a ‘container’ of the illicit drugs, and therefore illegal. A loophole further complicates the legal situation—the spores of psilocybin mushrooms do not contain the drugs, and are legal to possess in many areas. Jurisdictions that have specifically enacted or amended laws to criminalize the possession of psilocybin mushroom spores include Germany (since 1998), and California, Georgia, and Idaho in the United States. There is consequently an active underground economy involved in the sale of spores and cultivation materials, and an internet-based social network to support the illicit activity. After a long interruption in the use of psilocybin in research, there has been a general shift in attitudes regarding research with hallucinogenic agents. Many countries are revising their positions and have started to approve studies to test the physiological and therapeutic effects of hallucinogens.